Plate-fin and tube heat exchanger with a dog-bone and serpentine tube insertion

ABSTRACT

A dog-bone type heat exchanger having a plurality of fin members for dissipating heat. Each of the plurality of fin members includes a pair of offset surfaces interconnected by a sloped interconnecting surface. The plurality of fins members may be spaced apart at a distance that is less than, equal to, or more than the offset distance between the pair of offset surfaces on each fin member, thereby maximizing the mixing of air flow and the conductive heat transfer of the heat exchanger through an impinging effect.

FIELD OF THE INVENTION

[0001] The present invention generally relates to heat exchangers and,more particularly, relates to a heat exchanger having heat transferelements with improved heat transfer characteristics.

BACKGROUND OF THE INVENTION

[0002] Conventional heat exchangers of the plate fin-tube type generallyinclude of a plurality of parallel tubes having a plurality ofperpendicular fins. The plurality of perpendicular fins is thermallycoupled to the plurality of parallel tubes to serve as an evaporator.Heat absorbing fluid is forced through a capillary tube into theplurality of parallel tubes at a low temperature and pressure.Subsequent evaporation of the fluid removes heat energy from the airpassing adjacent the tubes of the evaporator, thus cooling the air. Thefins attached to the tube increase the effective heat absorbing areaover which the airflow is directed, thus increasing the coolingefficiency of the evaporator. A small motor driven fan is utilized todraw air over the heat absorbing area of the evaporator and dischargethe cooled air into the interior of the refrigerator.

[0003] Several attempts have been made to increase the coolingefficiency of the evaporator by varying the arrangement of the tubepattern and fin shape. U.S. Pat. No. 4,580,623 discloses a heatexchanger having parallel rows of serpentine tube coils slanting in thesame direction and using ultra thin fins having a pattern embossedthereon to induce turbulence in the airflow over the evaporator.However, the refrigeration industry is currently requiring a widerevaporator to increase the face area of the evaporator met by theairflow to reduce the effects of frost growth and thereby increase thecooling efficiency of the refrigerator system. To enhance the coolingefficiency it is possible to add additional rows of tubes or additionalfins to the evaporator. However, additional fins generally cause anarrowing of the space between fins, which may limit airflow therebetween and increase the amount of material necessary to manufacture theevaporator, thus increasing cost. Further, additional rows of fins mayalso lead to excessive air-pressure drops across the fins, especially asfrost accumulates on the fins and tubes.

[0004] A need to improve the cooling efficiency of the current findesign is particularly felt in the area of “dog-bone” type heatexchangers. Dog-bone type heat exchangers generally include a pluralityof fins each having a series of slots formed therein. These slots aregenerally in the shape of a dog bone—having generally circular endportions and a slightly narrower intermediate, connecting portion.Unlike other heat exchanger types, dog-bone heat exchangers employ asingle, continuous tube that is bent into a serpentine-like pattern,which traverse back and forth through the series of slots formed in thefins once assembled. This single, continuous tube eliminates the needfor complicated tube assembly, such as assembly and brazing of joints.The tube is bent into its preferred shaped prior to insertion throughthe dog-bone slots. Due to the narrower immediate portion of thedog-bone slots, the bends along at least one side of the final tubeshape are crimped to enable insertion of the tube into the fins. Thistube bundle is then inserted through the dog-bone slots to form theassembly. Traditionally, it is difficult to hold the fins in properposition during this insertion stage. Experience has shown that thisdifficulty is compounded if an irregularly shaped fin is used.

[0005] Dog-bone type heat exchangers are often used in refrigerationapplications, such as refrigerator-freezer applications. Refrigerationapplications typically use a lower airflow rate relative to commercialcooling systems. These lower airflow rates decrease the cooling capacityof the heat exchanger. Moreover, such refrigerator-freezer applicationsfurther require that frost be able to collect on the fins and tubes.Therefore, to minimize the chance of the fins being clogged with frost,the fins must be placed further apart to allow air to continue to passthrough the evaporator as the frost accumulates. This increaseseparation of the fins limits the number of fins used and, furthermore,reduces the mixing of the airflow around the fins, thereby reducing thecooling capacity of the system. However, irregularly shaped fins aredifficult to assemble with the continuous tube.

[0006] Accordingly, there exists a need in the relevant art to provide adog-bone type heat exchanger system having evaporator fins that permitthe accumulation of frost and the pass through of air, yet providesimproved cooling capacity. Furthermore, there exists a need in therelevant art to provide a dogbone type heat exchanger havingsufficiently spaced fins that provides improved mixing of the airflowaround such fins to improve cooling capacity. Still further, thereexists a need in the relevant art to provide a dog-bone type heatexchanger system having fins capable of improving the mixing of theairflow around such fins without adversely affecting the ease ofassembly. Lastly, there exists a need in the relevant art to provide adog-bone type heat exchanger system that overcomes the disadvantages ofthe prior art.

SUMMARY OF THE INVENTION

[0007] According to the principles of the present invention, a dog-bonetype heat exchanger is provided having an advantageous construction andmethod of assembly. The dog-bone type heat exchanger includes aplurality of fin members for dissipating heat. Each of the plurality offin members includes a pair of offset surfaces interconnected by asloped interconnecting surface. The plurality of fins members may bespaced apart at a distance that is less than, equal to, or more than theoffset distance between the pair of offset surfaces on each fin member.

[0008] Further areas of applicability of the present invention willbecome apparent from the detailed description provided hereinafter. Itshould be understood that the detailed description and specificexamples, while indicating the preferred embodiment of the invention,are intended for purposes of illustration only and are not intended tolimit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

[0010]FIG. 1 is a perspective view illustrating an evaporator accordingto the principles of the present invention;

[0011]FIG. 2 is an elevational view illustrating the evaporator of thepresent invention;

[0012]FIG. 3 is a front view illustrating the dog-bone slots;

[0013]FIG. 4 is a side view illustrating the profile configuration ofthe fin according to the present invention; and

[0014]FIG. 5 is a plan view illustrating the insertion of the tubebundle into a plurality of fins being secured within a jig member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The following description of the preferred embodiment is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

[0016] Referring to FIGS. 1-4, an evaporator system, generally indicatedat 10, is illustrated for use in a refrigeration system (not shown). Therefrigeration system generally includes a refrigerator having a spacedapart wall section forming a passageway. Evaporator system 10, inaccordance with the present invention, is placed in the passageway andis used to cool the air drawn over evaporator system 10 and isdischarged into the refrigerator by a fan. Evaporator system 10, whenused in a restaurant appliance, is generally operated at a temperaturesuch that frost tends to collect on the surfaces of the evaporator.Accordingly, evaporator system 10 must include pathways extending therethrough to permit the passage of air to prevent clogging of theevaporator. Should the evaporator system become clogged, the airflowover the evaporator is reduced causing an airside pressure drop and adecrease in the cooling efficiency of the device (i.e., reducing theairflow over evaporator system 10 reduces the amount of cool airdischarged into the refrigerator). In an attempt to keep therefrigerator at the desired temperature level, the system works harder(i.e., the compressor runs almost continuously to provide a supply ofheat absorbing fluid to evaporator system 10 in an attempt to provideadditional cool air to the refrigerator).

[0017] Evaporator system 10 of the preferred embodiment comprises acontinuous tube 12 having both inlet 14 and outlet 16 ends. Continuoustube 12 is formed in a serpentine configuration by a plurality ofreverse bends 18 and parallel tube runs 20. As best seen in FIGS. 1 and3, continuous tube 12 is folded into an essentially bi-planarconfiguration resulting in two adjacent rows of tubes 22, 24. Tube rows22, 24 are made up of sets of two parallel tubes 26, 28 with the exit ofeach set connected to the entrance of the next successive set in therespective row by a respective reverse bend 18. The sets of paralleltubes in each row 22, 24 are sloped in co-planar directions relative tothe longitudinal axis of tube row 22, 24.

[0018] As best seen in FIGS. 1, 3, and 4, fins 30 each include a varyingprofile capable of dramactically enhancing the mixing of the air flowpassing through evaporator system 10 and further capable of enhancingthe impingeing effect of air contacting each fin 30. With particularreference to FIGS. 3 and 4, fins 30 each includes a first surface 34 anda second surface 36. According to the present embodiment, first surface34 is a planar surface that is parallel to and offset from second planarsurface 36 as indicated at A. First surface 34 and second surface 36 areinterconnected via a sloping, interconnecting surface 38. Preferably,fin 30 further includes a plurality of first surfaces 34 and secondsurfaces 36 each interconnected in a similar manner by sloping,interconnecting surface 38. Most preferably, first surface 34 and secondsurface 36 alternate after each pair of slots 32, thereby providing themaximum number of alternating surfaces 34, 36, while maintaining agenerally flat surface adjacent slots 32 for assembly. This will bediscussed further below. It should be noted, however, that the exactdimensions and shape of fins 30 may be modified to accomodate theparticular needs of the intended application. The planar shape of firstsurface 34 and second surface 36 is preferably oriented perpendicular tothe direction of insertion of continuous tube 12.

[0019] Still referring to FIGS. 3 and 4, fins 30 are preferably made ofstamp-formed aluminum having a thickness of about 0.15 mm. Moreparticularly, fins 30 are preferably stamp-formed in a singlemanufacturing step to form the outer dimensions of fin 30, slots 32,first surface(s) 34, second surface(s) 36, and interconnectingsurface(s) 38. As best seen in FIG. 3, slots 32 each include a pair ofgenerally circular portions 40 having a generally narrower intermediateportion 42 extending between the pair of generally circular portions 40.Referring now to FIG. 4, the pair of generally circular portions 40 eachinclude an outwardly-turned collar portion 44 being stamp-formed toprovide a generally non-abrasive surface for contacting continuous tube12. Collar portion 44 further serves to provide an enlarged contactsurface area to improve conductive heat transfer between continuous tube12 and each fin 30.

[0020] Fins 30 are secured on continuous tube 12 by inserting bends 18of continuous tube 12 into canted slots 32 of fins 30. The overalllength of slot 32 is slightly less than the overall outer dimension ofthe set of two tubes. Since the overall length of the slot is slightlyless than the overall outer dimension of the set of two tubes, the tubesets are press fit into slots 32 to ensure metal-to-metal contact, whichenhances heat conduction between the tube walls and fins 30. Fins 30 areevenly spaced on tube 12 and when used in refrigeration units arenormally spaced three-to-six fins per inch of tube.

[0021] As best seen in FIG. 5, assembly of fins 30 and continuous tube12 is facilitated with the use of a jig member 46. Jig member 46generally includes a base portion 48 and a plurality of support rails50. The plurality of support rails 50 being generally orthogonal to baseportion 48 and include a series of complimentary angled channels 52 toengage interconnecting surface 38 of fins 30. Accordingly, bends 18 ofcontinuous tube 12 are inserted into respective slots 32 of fins 30,channels 52 of support rails 50 cooperate to retain fins 30 in properposition and spacing. Once insertion is complete, the final evaporatorsystem 10 may be removed from jig member 46.

[0022] The cooling efficiency of evaporator system 10 of the presentinvention may be further improved over conventional designs as a resultof the particular offset and profile of fins 30. With reference to FIG.4, an example of the planar-offset configuration of fins 30 isillustrated. Although it should be appreciated that fins 30 may bespaced apart any distance that is found to maximize heat exchange, inthis example fin 30 and an adjacent fin 30′ are offset a distance B thatis at least less than or equal to the offset distance A between firstsurface 34 and second surface 36. Moreover, again relative to thisparticular example, distance B remain less than or equal to distance Adespite various fin shapes. Such an arrangement leads to improved mixingof airflow C passing between fin 30 and fin 30′. In other words, sucharrangement eliminates any straight through passage lines extendingbetween adjacent fins, thereby requiring mixing of airflow andmaximizing the amount of air molecules impinging upon interconnectingsurfaces 38. The impinging of air molecules on interconnecting surfaces38 improves the heat transfer between the air and continuous tube 12,thus improving the cooling efficiency of evaporator system 10. Byimproving the cooling efficiency, the amount of work required may bereduced and/or the spacing of fins 30 may be increased to facilitate theflow of air between adjacent fins 30 as frost accumulates on fins 30.

[0023] It has been seen that as air is drawn over evaporator system 10,the air impinges the cooling fins and further mixes, thereby increasingthe cooling effect and efficiency of evaporator system 10 over prior artevaporators having flat fin designs. Accordingly, the invention resultsin lower manufacturing costs, since unnecessary fins may be removed.Furthermore, as a result of the option to use increased spacing betweenadjacent fins, the pressure drop is minimized, which enables the use ofa smaller fan and compressor motor, thus decreasing operating costs andnoise.

[0024] However, in summary, it is important to note that preferably thefins of the present invention include a plurality of offset planarsurfaces. These offset planar surface preferably alternative betweeneach pass of the tubing, thus maximizing the number of alternatingsurface while still maintaining the necessary perpendicular relationshipwith the tubing. This perpendicular relationship eases assembly in thata plurality of fins may be easily held in a jig at which time thepreformed serpentive tubing is easily inserted.

[0025] The description of the invention is merely exemplary in natureand, thus, variations that do not depart from the gist of the inventionare intended to be within the scope of the invention. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A dog-bone type heat exchanger comprising: afirst fin member having a first surface and a second surfaceinterconnected by a first sloped interconnecting surface, a plane ofsaid first surface being offset from a plane of said second surface; asecond fin member having a third surface and a fourth surfaceinterconnected by a second sloped interconnecting surface, a plane ofsaid third surface being offset from a plane of said fourth surface; aplurality of slots formed through said first surface and said thirdsurface, each of said plurality of slots having a pair of generallycircular portions and an intermediate portion; a continuous tube forconveying a first fluid within said tube to exchange heat with a secondfluid surrounding said tube, said tube having a plurality of reversebends forming a plurality of parallel tube runs, said tube being coupledto said first fin member and said second fin member such that each ofsaid plurality of reverse bends passes through a corresponding one ofsaid plurality of slots formed in said first fin member and said secondfin member.
 2. The dog-bone type heat exchanger according to claim 1,further comprising: a collar portion extending about the periphery ofeach of said plurality of generally circular portions of said pluralityof slots, said collar portions generally facilitating heat conductionand minimizing abrasion between said first and second fin members andsaid continuous tube.
 3. The dog-bone type heat exchanger according toclaim 1 wherein a distance between said plane of said first surface andsaid plane of said second surface is at least equal to or greater than adistance between said first fin member and said second fin member. 4.The dog-bone type heat exchanger according to claim 1, furthercomprising: said plurality of slots further being formed through saidsecond surface and said fourth surface to receive said plurality ofreverse bends.
 5. The dog-bone type heat exchanger according to claim 1wherein the width of said intermediate portion is smaller than adiameter of each of said pair of generally circular portions
 6. A methodof assemblying a dog-bone type heat exchanger, said method comprising:providing a base member having a plurality of spaced support memberscoupled thereto forming support channels therebetween; providing a pairof fin members each having a first surface and a second surfaceinterconnected by a first sloped interconnecting surface, a plane ofsaid first surface being offset from a plane of said second surface, atleast said first surface having a plurality of slots formedtherethrough, each of said plurality of slots having a pair of generallycircular portions and an intermediate portion; inserting each of saidpair of fin members into said corresponding support channels formed insaid base member; providing a continuous tube having a plurality ofreverse bends forming a plurality of parallel tube runs; and insertingeach of said plurality of reverse bends through a corresponding one ofsaid plurality of slots formed in said pair of fin members.
 7. Themethod of assemblying a dog-bone type heat exchanger according to claim6 wherein said step of inserting each of said pair of fin members intosaid corresponding support channels formed in said base member includesretaining each of said pair of fin members along only saidinterconnecting surface using only said support channel.
 8. The methodof assemblying a dog-bone type heat exchanger according to claim 6wherein said step of providing a pair of fin members includes providingsaid pair of fin members wherein the width of said intermediate portionis smaller than a diameter of each of said pair of generally circularportions, thereby generally defining a dog-bone shape.
 9. The method ofassemblying a dog-bone type heat exchanger according to claim 6, furthercomprising: spacing said pair of fin members a distance that is greaterthan or equal to a distance between said plane of said first surface andsaid plane of said second surface.
 10. A dog-bone type heat exchangercomprising: a first fin member having a first surface and a secondsurface interconnected by a first sloped interconnecting surface, aplane of said first surface being offset from a plane of said secondsurface; a second fin member having a third surface and a fourth surfaceinterconnected by a second sloped interconnecting surface, a plane ofsaid third surface being offset from a plane of said fourth surface; aplurality of slots formed through said first surface and said thirdsurface, each of said plurality of slots having a pair of generallycircular portions and an intermediate portion, said intermediate portionhaving a width smaller than a diameter of each of said pair of generallycircular portions; a continuous tube for conveying a first fluid withinsaid tube to exchange heat with a second fluid surrounding said tube,said tube having a plurality of reverse bends forming a plurality ofparallel tube runs, said tube being folded into a tube bundle, said tubebundle being coupled to said first fin member and said second fin membersuch that each of said plurality of reverse bends passes through acorresponding one of said plurality of slots formed in said first finmember and said second fin member, wherein a distance between said planeof said first surface and said plane of said second surface is at leastequal to or greater than a distance between said first fin member andsaid second fin member.
 11. The dog-bone type heat exchanger accordingto claim 10, further comprising: a collar portion extending about theperiphery of each of said plurality of generally circular portions ofsaid plurality of slots, said collar portions generally facilitatingheat conduction and minimizing abrasion between said first and secondfin members and said continuous tube.
 12. The dog-bone type heatexchanger according to claim 10, further comprising: said plurality ofslots further being formed through said second surface and said fourthsurface to receive said plurality of reverse bends.